The present invention relates to methods and compositions for increasing the viscosity of a fluid. More particularly, the present invention relates to boronic acid crosslinking agents, viscosified treatment fluids, and methods of using these compositions in applications wherein viscosified fluids may be used.
Many industrial applications require viscosified fluids or “viscosified treatment fluids.” For instance, the upstream energy industry uses viscosified treatment fluids in a variety of production and stimulation operations. For example, such fluids may be used as drilling fluids, fracturing fluids, and gravel packing fluids.
Viscosified treatment fluids that are used in subterranean operations generally are aqueous-based fluids that comprise gelling agents. These gelling agents may comprise biopolymers or synthetic polymers. Common gelling agents include, e.g., galactomannan gums, cellulosic polymers, and polysaccharides.
Most viscosified treatment fluids include crosslinked gelling agent molecules to increase their viscosity. The crosslinking between gelling agent molecules occurs through the action of a crosslinking agent. These crosslinking agents may comprise a metal, transition metal, or metalloid, collectively referred to herein as “metal(s).” Examples include boron, aluminum, antimony, zirconium, magnesium, or titanium. Generally, the metal of a crosslinking agent interacts with at least two gelling agent molecules to form a crosslink between them, thereby forming a crosslinked gelling agent.
Crosslinking agents often comprise boron because it is compatible with a number of gelling agents used in viscosified treatment fluids. These boron-containing crosslinking agents, however, generally are limited to viscosified treatment fluids used in environments that have a pH of about 8 and above and a temperature below about 300° F. This pH requirement may preclude using salt water in the viscosified treatment fluid. Similarly, viscosified treatment fluids comprising gelling agents that are crosslinked with boron-containing crosslinking agents may suffer from thermal instability at certain elevated temperatures, like those frequently encountered in some subterranean operations. In addition, boron-containing crosslinking agents often react with additives commonly used with treatment fluids, e.g., glycols (such as ethylene or propylene glycol) or alcohols (such as methanol). To overcome this propensity, boron crosslinking agents typically are added in excess to treatment fluids, which may increase the environmental footprint and the costs associated with the treatment fluid.